How Does Phylogeny Help Us Classify and Understand Organisms?
What is Phylogeny?
Phylogeny can be defined as an evolutionary history of a species or group as there are about 100 million species living on earth today. The morphological and biochemical evidence suggests that all the organisms are genetically related. A situation where the genealogical relationships of the organisms can be represented in the form of an evolutionary tree, that is termed as a Phylogenetic tree. In this, the species or groups are organized in such a way that it helps to know how they evolved from the common ancestors. Phylogeny helps in the details of how the genes, genomes and species evolve. It is useful for fundamental and numerical applications.
Phylogenetic Trees
The phylogenetic tree is also known as the cladogram. The species or the groups are found at the tips of the lines known as the tree branches. The evolution of species evolved from a common ancestor is exhibited by how the branches connect. The branch points represent the most recent common ancestor of all the groups descended from that common point. Some cladograms are blocky, while the others are diagonal. However, the orientation of the tree does not change the information. In a phylogenetic tree, if two species have the more common recent ancestor, they are more related than those with a less recent common ancestor.
Applications of Phylogenetics
Phylogenetics has the following applications:-
Classification
With the help of phylogeny, the Linnaean classification of species is known. Based on the sequence data, more accurate descriptions of patterns of relatedness are available.
Forensics
The DNA in case of a crime scene or paternity disputes is assessed by phylogeny.
Identification of the Origin of Pathogens
Phylogenetic approaches can be used to know about a new pathogen outbreak. It helps to know the species the pathogen is related to and the source of its transmission.
Conservation
Phylogeny helps the conservation biologists to make the correct decisions about which species they should try to prevent extinction.
Computing and Bioinformatics
The algorithms developed for phylogenetics are also used in software development in other fields.
Ontogeny and Phylogeny
Ontogeny is the course of development of an individual organism. It begins at the time of fertilization and includes all the developmental events at the time of birth and thereafter.
The ancestral characters are often preserved in the development of an organism. For eg., the chick and human embryos generally undergo a stage during their development wherein they have slits and arches in their neck similar to the gill slits and arches of a fish. This suggests that humans and chicks share a common ancestor with fish. These developmental characters can be used to create phylogenetic trees.
It is believed that during development, an organism progresses through each of the adult stages of evolutionary history. This states that “ontogeny recapitulates phylogeny”. For instance, a chick goes through the following stages of evolutionary history during the development- a single cell, a multicellular invertebrate, fish, reptile, bird, and then forms the chick. However, the statement is controversial and cannot be proved in all the organisms.
For some years, the organisms have evolved into more derivative forms. The new generations retain most of their ancestral features. It becomes easy for them to get adjusted in the environment they live in as these features get modified with additional novel traits. Phylogeny helps us to know the similarities and differences between plants, animals, and microorganisms.
Difference Between Ontogeny and Phylogeny
The development of an organism is defined as Ontogeny while phylogeny refers to how the organisms have evolved.
Let us take an example of a chicken, the ontogeny will explain the entire development cycle of the chicken right from the single cell. Now let's take an example of an ostrich and assume that it descended from the family of chickens, phylogeny will explain how the chicken evolved into an ostrich, i.e., it will explain the evolutionary process.
FAQs on Phylogeny in Biology: Meaning, Applications & Examples
1. What is phylogeny in biology?
Phylogeny is the study of the evolutionary history and relationships among different groups of organisms. Its primary goal is to understand how species or other taxa are related to each other through common descent. This is often reconstructed using morphological, biochemical, and genetic data to trace the lines of ancestry over geological time.
2. What is a phylogenetic tree and what do its components represent?
A phylogenetic tree is a branching diagram that visually represents the evolutionary relationships among various biological species. Its key components are:
- Branches: These represent the evolutionary lineages or the passage of genetic information through time.
- Nodes: These are points where a branch splits, representing a common ancestor from which two or more new lineages diverged.
- Tips (or Terminal Nodes): These represent the individual organisms, species, or groups (taxa) being studied.
- Root: This is the base of the tree and represents the most recent common ancestor of all the organisms in the tree.
3. How is DNA evidence used to determine phylogenetic relationships?
DNA-based phylogeny, or molecular phylogenetics, works on the principle that as organisms evolve, their DNA sequences accumulate mutations. By comparing the DNA sequences of different species (for example, specific genes like ribosomal RNA), scientists can measure their degree of genetic similarity. Species with more similar DNA sequences are considered to be more closely related, as they have had less time to diverge from a recent common ancestor.
4. What is the difference between phylogeny and taxonomy?
While related, phylogeny and taxonomy are distinct fields. Taxonomy is the science of naming, describing, and classifying organisms into a hierarchical system (e.g., Kingdom, Phylum, Class). Phylogeny, on the other hand, is the study of their evolutionary history and relatedness. Modern taxonomy aims to be phylogenetic, meaning the classification groups should reflect true evolutionary relationships discovered through phylogenetic analysis.
5. How does understanding phylogeny help in conservation biology?
Phylogeny is crucial for conservation biology because it helps identify and prioritise species for protection. By analysing the evolutionary tree, conservationists can:
- Identify species that are genetically unique and have no close relatives, making them a higher priority for conservation.
- Maximise the preservation of phylogenetic diversity, which is the total amount of evolutionary history represented in a group of species.
- Make informed decisions about managing populations to maintain genetic health and evolutionary potential.
6. What is the difference between homologous and analogous structures in the context of phylogeny?
This distinction is critical for building accurate phylogenetic trees. Homologous structures are features shared by related species because they have been inherited from a common ancestor (e.g., the forelimbs of humans, bats, and whales). These are strong evidence of a close phylogenetic relationship. In contrast, analogous structures are features that have a similar function but evolved independently in different lineages due to similar environmental pressures, a process called convergent evolution (e.g., the wings of a bird and an insect). Analogous structures do not indicate a close evolutionary relationship.
7. What are some real-world applications of phylogenetics?
Beyond academic classification, phylogenetics has several practical applications:
- Epidemiology: Tracking the origin, spread, and evolution of infectious diseases like COVID-19, HIV, and influenza by analysing the genetic changes in the pathogen.
- Forensics: Identifying the source of a biological sample in a criminal case or tracing the origin of illegally traded wildlife products.
- Agriculture: Identifying wild relatives of crops that may possess beneficial traits like disease resistance, which can be used in breeding programs.
- Drug Discovery: Predicting the function of unknown genes or proteins based on their relationship to known ones in other species.
8. What is the meaning of the phrase 'ontogeny recapitulates phylogeny' and is it accurate?
The phrase 'ontogeny recapitulates phylogeny' was proposed by Ernst Haeckel and suggests that the development of an organism from embryo to adult (ontogeny) goes through stages resembling the adult forms of its evolutionary ancestors (phylogeny). For example, human embryos temporarily have structures resembling gill slits. However, this theory is now considered an oversimplification and is largely inaccurate. While embryos of related species do show similarities reflecting common ancestry, they do not replay the adult forms of their ancestors.
9. Why is a rooted phylogenetic tree considered more informative than an unrooted one?
An unrooted tree illustrates the relatedness of the organisms but does not show the direction of evolution or the position of the last common ancestor. A rooted tree is more informative because it includes a common ancestor for all organisms in the tree (the root), which is often determined by including an 'outgroup' (a more distantly related species). This root provides a timeline and a clear direction of evolutionary events, showing which lineages are older and which have diverged more recently.
